index(in, find)
awk 'BEGIN { print index("peanut", "an") }'prints `3'. If find is not found,
index
returns 0. (Remember that string indices in awk
start at 1.)length(string)
length("abcde")
is 5. By contrast, length(15 * 35)
works out to 3. How? Well, 15 * 35 = 525, and 525 is then converted to the string `"525"', which has three characters. If no argument is supplied, length
returns the length of $0
. In older versions of awk
, you could call the length
function without any parentheses. Doing so is marked as "deprecated" in the POSIX standard. This means that while you can do this in your programs, it is a feature that can eventually be removed from a future version of the standard. Therefore, for maximal portability of your awk
programs you should always supply the parentheses. match(string, regexp)
match
function searches the string, string, for the longest, leftmost substring matched by the regular expression, regexp. It returns the character position, or index, of where that substring begins (1, if it starts at the beginning of string). If no match if found, it returns 0. The match
function sets the built-in variable RSTART
to the index. It also sets the built-in variable RLENGTH
to the length in characters of the matched substring. If no match is found, RSTART
is set to 0, and RLENGTH
to -1. For example: awk '{This program looks for lines that match the regular expression stored in the variable
if ($1 == "FIND")
regex = $2
else {
where = match($0, regex)
if (where)
print "Match of", regex, "found at", where, "in", $0
}
}'
regex
. This regular expression can be changed. If the first word on a line is `FIND', regex
is changed to be the second word on that line. Therefore, given:FIND fo*bar
My program was a foobar
But none of it would doobar
FIND Melvin
JF+KM
This line is property of The Reality Engineering Co.
This file created by Melvin.
awk
prints:Match of fo*bar found at 18 in My program was a foobar
Match of Melvin found at 26 in This file created by Melvin.
split(string, array, fieldsep)
array[1]
, the second piece in array[2]
, and so forth. The string value of the third argument, fieldsep, is a regexp describing where to split string (much as FS
can be a regexp describing where to split input records). If the fieldsep is omitted, the value of FS
is used. split
returns the number of elements created. The split
function, then, splits strings into pieces in a manner similar to the way input lines are split into fields. For example: split("auto-da-fe", a, "-")splits the string `auto-da-fe' into three fields using `-' as the separator. It sets the contents of the array
a
as follows:a[1] = "auto"The value returned by this call to
a[2] = "da"
a[3] = "fe"
split
is 3. As with input field-splitting, when the value of fieldsep is " "
, leading and trailing whitespace is ignored, and the elements are separated by runs of whitespace.sprintf(format, expression1,...)
printf
would have printed out with the same arguments (see section Using printf
Statements for Fancier Printing). For example: sprintf("pi = %.2f (approx.)", 22/7)returns the string
"pi = 3.14 (approx.)"
.sub(regexp, replacement, target)
sub
function alters the value of target. It searches this value, which should be a string, for the leftmost substring matched by the regular expression, regexp, extending this match as far as possible. Then the entire string is changed by replacing the matched text with replacement. The modified string becomes the new value of target. This function is peculiar because target is not simply used to compute a value, and not just any expression will do: it must be a variable, field or array reference, so that sub
can store a modified value there. If this argument is omitted, then the default is to use and alter $0
. For example: str = "water, water, everywhere"sets
sub(/at/, "ith", str)
str
to "wither, water, everywhere"
, by replacing the leftmost, longest occurrence of `at' with `ith'. The sub
function returns the number of substitutions made (either one or zero). If the special character `&' appears in replacement, it stands for the precise substring that was matched by regexp. (If the regexp can match more than one string, then this precise substring may vary.) For example:awk '{ sub(/candidate/, "& and his wife"); print }'changes the first occurrence of `candidate' to `candidate and his wife' on each input line. Here is another example:
awk 'BEGIN {prints `dcaacbaaa'. This show how `&' can represent a non-constant string, and also illustrates the "leftmost, longest" rule. The effect of this special character (`&') can be turned off by putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write `\\&' in a string constant to include a literal `&' in the replacement. For example, here is how to replace the first `|' on each line with an `&':
str = "daabaaa"
sub(/a*/, "c&c", str)
print str
}'
awk '{ sub(/\|/, "\\&"); print }'Note: as mentioned above, the third argument to
sub
must be an lvalue. Some versions of awk
allow the third argument to be an expression which is not an lvalue. In such a case, sub
would still search for the pattern and return 0 or 1, but the result of the substitution (if any) would be thrown away because there is no place to put it. Such versions of awk
accept expressions like this:sub(/USA/, "United States", "the USA and Canada")But that is considered erroneous in
gawk
.gsub(regexp, replacement, target)
sub
function, except gsub
replaces all of the longest, leftmost, nonoverlapping matching substrings it can find. The `g' in gsub
stands for "global," which means replace everywhere. For example: awk '{ gsub(/Britain/, "United Kingdom"); print }'replaces all occurrences of the string `Britain' with `United Kingdom' for all input records. The
gsub
function returns the number of substitutions made. If the variable to be searched and altered, target, is omitted, then the entire input record, $0
, is used. As in sub
, the characters `&' and `\' are special, and the third argument must be an lvalue.substr(string, start, length)
substr("washington", 5, 3)
returns "ing"
. If length is not present, this function returns the whole suffix of string that begins at character number start. For example, substr("washington", 5)
returns "ington"
. This is also the case if length is greater than the number of characters remaining in the string, counting from character number start. tolower(string)
tolower("MiXeD cAsE 123")
returns "mixed case 123"
. toupper(string)
toupper("MiXeD cAsE 123")
returns "MIXED CASE 123"
.